Angiotensin II, corticosteroids, type II diabetes and the metabolic syndrome

SummarySyndrome X, the Metabolic Syndrome, and type II diabetes are closely related diseases that share risk factors and symptoms, notably insulin resistance. Several factors have been proposed either to mediate the disease(s) or to be their causes, and most converge on the endocrine/paracrine functions of the adipocyte. A common feature of such systems is their relative autonomy from systemic negative feedback regulation, for example by the HPA axis. We draw particular attention to two such mechanisms, both of which are associated with, and can cause, insulin resistance: the extra-adrenal production of corticosteroids, and the tissue renin angiotensin system of the adipocyte. These show another feature: the inter-regulation of glucocorticoid action and the RAS by positive feedback. Cortisol enhances the expression of 11β-HSD 1, and also of angiotensinogen and angiotensin type 1 receptors. In turn, angiotensin can stimulate further corticosteroid production, from the adrenal and perhaps from extra-adrenal sources. The instability inherent in such positive loops could account for the progressive nature of the disease(s), suggesting ways to break the circle.